A finite binary string is a finite string of $0$s and $1$s$.$ For example, $01101$ is a binary string of length $5.$

$($a$)$ What is the cardinality of the set of binary strings that have length exactly n$?$

$($b$)$ What is the cardinality of the set of binary strings that have length less than or equal to n$?$

$($c$)$ What is the cardinality of the set of all finite binary strings